Process and system for converting carbonaceous feedstocks into energy without greenhouse gas emissions

ABSTRACT

The process and system of the invention converts carbonaceous feedstock such as coal, hydrocarbon oil, natural gas, petroleum coke, oil shale, carbonaceous-containing waste oil, carbonaceous-containing medical waste, carbonaceous-containing military waste, carbonaceous-containing industrial waste, carbonaceous-containing medical waste, carbonaceous-containing sewage sludge and municipal solid waste, carbonaceous-containing agricultural waste, carbonaceous-containing biomass, biological and biochemical waste, and mixtures thereof into electrical energy without the production of unwanted greenhouse emissions. The process and system uses a combination of a gasifier, e.g., a kiln, operating in the exit range of at least 700° to about 1600° C. (1300-2900° F.) to convert the carbonaceous feedstock and a greenhouse gas stream into a synthesis gas comprising mostly carbon monoxide and hydrogen without the need for expensive catalysts and or high pressure operations. One portion of the synthesis gas from the gasifier becomes electrochemically oxidized in an electricity-producing fuel cell into an exit gas comprising carbon dioxide and water. The latter is recycled back to the gasifier after a portion of water is condensed out. The second portion of the synthesis gas from the gasifier is converted into useful hydrocarbon products..

[0001] This application is a continuation-in-part of application U.S.Ser. No. 10/602,536 filed Jun. 23, 2003 and U.S. Ser. No. 10/184,264filed Jun. 27, 2002 (published as Publication No. 2003/0022035 on Jan.30, 2003). This application is related to and contains common subjectmatter with U.S. Ser. No. 09/186,766 filed Nov. 5, 1998; now U.S. Pat.No. 6,187,465 issued Feb. 13, 2001 (the '465 patent), which claims thebenefit of U.S. provisional application Serial No. 60/064,692 filed Nov.7, 1997. This application is not a continuation-in-part of the latterapplication, U.S. Ser. No. 09/186,766, as stated in the parentapplication, U.S. Ser. No. 10/184,264.

[0002] This invention relates to non-greenhouse gas emitting processesand systems which accomplish the conversion of a carbonaceous gas streamand a greenhouse gas into a synthesis gas comprising hydrogen and carbonmonoxide without the need for expensive catalysts and or high pressureoperations.

BACKGROUND OF THE INVENTION

[0003] The burning of fossil fuels in boilers to raise high temperature,high-pressure steam that can be used to power turbo-electric generatorsproduces a problem source of carbon dioxide and other greenhouse gases,e.g. methane, ozone and fluorocarbons. This fossil fuel combustion,especially of coal, needs a technological fix to avoid the emission ofcarbon dioxide and other greenhouse gases with their attendantundesirable release to the earth's atmosphere resulting in theabsorption of solar radiation known as the greenhouse effect. Much ofthe world depends on coal for power. There have been significant effortsto develop clean coal technologies to greatly reduce the release of acidgases, such as sulfur oxides and nitrogen oxides. However, to date noneof these clean coal programs aim to eliminate the emissions of carbondioxide and other greenhouse gases. Efforts to use pure oxygen in powerplants and gasification systems to avoid the diluting effects ofnitrogen and to achieve higher efficiency suffers from the unacceptablecost of requiring an air separation plant and the problems of excessivetemperatures in oxygen-fed combustion turbo-generators.

[0004] There is also widespread effort to increase the efficiency ofpower plants by utilizing advanced thermodynamic combined cycles, moreefficient turbo-generators, improved condensers and cooling towers, andsimilar systems. A small portion of this effort involves the use offossil fuel gasification processes, which are highly efficient becausethey avoid combustion and large combustion product emissions. Finallythere is an effort by Westinghouse (Corporate literature, “SureCell®”1996 ) and others to combine the use of advanced high temperatureturbo-generators and fuel cells to accomplish conversion to electricityat about 70% instead of current conventional combined cycle power plantsof about 47%.

[0005] Today there is worldwide concern that the atmospheric buildup ofcarbon dioxide and other greenhouse gases will start to have seriousenvironmental consequences for the earth's tropospheric temperature,global rainfall distribution, water balance, severe weather storms, andsimilar consequences. Technological solutions are being demandedthroughout the world.

[0006] The worldwide research establishment, encouraged by governmentfunding from various agencies, continues to be focused on identifyingcommercially attractive gas separation technologies to remove carbondioxide from stack gases and also attractive chemistry that will utilizethis carbon dioxide as a raw material to manufacture useful products.This has, indeed, been a very large challenge with poor successes assummarized by the review papers; see Michele Aresta, and EugenioQuaranta, “Carbon Dioxide: A Substitute for Phosgene,” Chem.Tech. pp.32-40, March 1997. and Bette Hileman, “Industry Considers CO ₂ ReductionMethods”, Chem & Engr. News, pg. 30, Jun. 30, 1997. Trying to scrub theCO₂ from stack gases and trying to chemically react the recovered CO₂clearly is not the right path of research because of the technicaldifficulty and the process expense of reacting carbon dioxide.

SUMMARY OF THE INVENTION

[0007] The process and system of the invention converts carbonaceousfeedstock from fossil fuels and other combustible materials into energywithout the production of unwanted greenhouse emissions. The presentprocess comprises the following steps:

[0008] (a) converting a carbonaceous feedstock and a greenhouse gasstream in a gasification unit to synthesis gas comprising mainly carbonmonoxide and hydrogen, where the gasification unit is a non-catalytichigh temperature, gas-phase reactor operating at conditions to achieve agas exit temperature of from at least 700° to about 1600° C. (1300-2900°F.);

[0009] (b) electrochemically oxidizing at least a portion of thesynthesis gas from the gasification unit in a first half-cell of a fuelcell to produce a first half-cell exit gas comprising carbon dioxide andwater;

[0010] (c) recovering the carbon dioxide from the first half-cell exitgas to serve as a greenhouse gas stream in step (a); and

[0011] (d) electrochemically reducing an oxygen-containing gas in asecond half-cell of the fuel cell completing the circuit and resultingin the production of electrical energy.

[0012] In contrast to the present invention, the invention disclosed andclaimed in the '465 patent preferably used a gasification unitcontaining a catalyst that operates at a temperature in the range ofabout 400° to about 700° C. (750-1300° F.) and still more preferably, agasification unit using a fluidized catalytic bed. The requirement forthe use of a catalytic bed requires expensive catalysts and/orhigh-pressure operations. The catalysts, e.g., nickel or copper-basedceramic supported catalyst typically used in steam reforming of methaneor shift converters are easily poisoned by halogens or heavy metalsfound in waste streams that are a desirable candidate forwaste-to-energy-systems. Although catalysts allow for significantreductions in the gas-phase temperature to carry out the synthesis gasformation chemistry, these catalysts only function as long as theyremain active and not poisoned by low level contaminates found in thewaste feedstocks.

[0013] The present system comprises the following:

[0014] (a) the gasification unit that is a non-catalytic hightemperature, gas-phase reactor operating at conditions to achieve a gasexit temperature of from at least 700° to about 1600° C. (1300 to 2900°F.), f6r converting a carbonaceous and a greenhouse gas stream feedstockinto the synthesis gas;

[0015] (b) the fuel cell for the production of electrical energycomprising the first half-cell having an inlet in fluid communicationwith the synthesis gas and a first means or anode for electrochemicallyoxidizing synthesis gas into the first half-cell exit gas, a secondhalf-cell having a second means or cathode for electrochemicallyreducing the oxygen-containing gas, and a membrane separating the firstand second half cells that will not allow passage of the gaseouscomponents from the respective half-cells; and

[0016] (c) passage means for passing the carbon dioxide from the firsthalf-cell to serve as a greenhouse gas stream for the gasification unit.

[0017] Preferably the non-catalytic, gas-phase reactor is a kiln havingan inlet means, a gas outlet means, and a solids outlet between theinlet means and the gas outlet means and operating at a temperaturegradient along the length of the kiln of about 200° to about 1600° C.(400-2900° F.).

[0018] The present process avoids the difficult path of attempting tostrip and capture the carbon dioxide from stack gases and withoutattempting to carry out separate chemical reactions of carbon dioxide toattempt to produce useful products. The process and system of thepresent invention uses unique gasification technology combined with fuelcells to generate electricity at high efficiency. This is accomplishedby taking advantage of a very unique property of fuel cells—namely, thetwo anodic and cathodic reactions are separated by an electronicallyconducting membrane that keeps the product gases separate. In this way,a combustible feed gas can be fully oxidized in the first half-cell ofthe fuel cell without being commingled with the final products of theair reduction in the second half-cell electrode, i.e., N₂. For example,in coal gasification, synthesis gas is formed consisting predominantlyof hydrogen and carbon monoxide. This synthesis gas is fed into thefirst half-cell, i.e., the anode or negative terminal side, of the fuelcell, such as the solid oxide or molten carbonate types, where it isoxidized to water and carbon dioxide. These gases are not diluted by thetypical nitrogen remaining after oxygen reduction in the second orremaining half-cell, i.e., the cathode side or positive terminal, of thefuel side. Nitrogen and combustion gases are commingled when combustionair is used in boilers or furnaces. Thus, in the fuel cell, thesynthesis gas (syngas) is oxidized without being combusted with air andwithout being diluted by other gases. The fuel cell-produced water andcarbon dioxide are simply separated from each other by condensing theliquid water and allowing the carbon dioxide to return to the gasifier.The carbon dioxide being injected into the high temperature gasifierundergoes a reaction with the high temperature carbonaceous feed to formmore carbon monoxide, repeating the cycle.

[0019] By means of the present process and system, the carbon dioxide inthe fuel cell is easily kept separate from the air side and anynitrogen. This carbon dioxide can be recycled back to the gasifier innearly pure form. Likewise steam in pure form can be recycled as well indifferent amounts under gasifier control system requirements to maintainthe ideal hydrogen to carbon monoxide ratio in the range of about 1.75to about 2.5. This helps maintain a high hydrogen content in thegasifier so that a portion of the gasifier-produced syngas can be useddownstream in a chemical reactor such as a Fischer-Tropsch reactionsystem for the production of a variety of useful chemicals ranging frommethanol to paraffin waxes. These in turn are used to make usefulchemicals such as naphtha, gas oil, and kerosine, or agriculturalchemicals or carbide abrasives. The latter are not ever burned in theirlifecycle, and they sequester the carbon forever. Thus, the carbonmonoxide is used to produce useful chemicals instead of discarding thevaluable carbon source in the carbon dioxide. The carbon balance of theplant is maintained such that the mass of carbon input in the waste feedis equal to the carbon mass leaving the plant as valuable hydrocarbonproducts; not carbon dioxide.

[0020] What has been achieved is a chemical plant merged with a powerplant that produces useful hydrocarbon products, high efficiencyelectric power without any carbon dioxide or other greenhouse gasemissions. And, most importantly gasification is much more flexible thana refinery or a coal boiler, since a wide variety of waste streams canbe used as the feed material. Thus, this solves two serious problems.

[0021] The process of the present invention is designed for use in awaste-to-energy plant using carbonaceous feedstocks such as coal;hydrocarbon oil; natural gas; petroleum coke; oil shale;carbonaceous-containing waste oil; carbonaceous-containing medicalwaste; carbonaceous-containing military waste including explosives,spent armaments, chemical and biological weapons agents, and unexplodedordinance; carbonaceous-containing industrial waste including hazardouswaste, insecticides, pesticides, fumicides, algaecides, and the like;carbonaceous-containing sewage sludge and municipal solid waste (MSW);carbonaceous-containing agricultural waste; carbonaceous-containingbiomass, biological and biochemical waste; and mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Advantages of the present invention will become apparent to thoseskilled in the art from the following description and accompanyingdrawings in which:

[0023]FIG. 1 is a schematic process flow diagram of a preferredembodiment of the process and system of the present invention;

[0024]FIG. 2 is a plot of the commercial steam reforming of methane tomake syngas consisting of hydrogen and carbon monoxide;

[0025]FIG. 3 shows a plot of the steam reforming of a mixture methaneand fuel cell produced carbon dioxide at about 20% in the feed;

[0026]FIG. 4 shows a plot of the steam reforming of a mixture methaneand fuel cell produced carbon dioxide at 25% in the feed;

[0027]FIG. 5 shows a plot of the steam reforming methane and fuel cellproduced carbon dioxide at 30% in the feed;

[0028]FIG. 6 shows a plot of the steam reforming methane and fuel cellproduced carbon dioxide at 27.6% in the feed with elevated steam at36.7%;

[0029]FIG. 7 shows a plot of the steam reforming of a mixture of atypical industrial waste, but without fuel cell produced carbon dioxideadded in the feed, with stoichiometric steam at 49.45%;

[0030]FIG. 8 shows a plot of the steam reforming of a mixture of atypical industrial waste, but without fuel cell produced carbon dioxideadded in the feed, with super-stoichiometric steam at 66%;

[0031] FIGS. 9-10 show plots of the steam reforming of a mixture of atypical industrial waste and fuel cell produced carbon dioxide at leastabout 20% added in the feed with super-sub steam at 46-51% achievinghigh hydrogen and the cleanest syngas in accordance with the preferredembodiment of the present invention;

[0032]FIG. 11 show a cross-sectional view of a superheater; and

[0033]FIG. 12 is a schematic diagram of a preferred gasifier as shown inFIG. 1 in which a rotary kiln is combined with a superheater shown inFIG. 11 so that the superheater is positioned within the exit region ofthe kiln in order to elevate the gas temperature and enrich the syngasexiting the kiln.

DETAILED DESCRIPTION OF THE INVENTION

[0034] Preferred Embodiment of Process for Hydrogen Fuel Cell EnergyWithout Production of Unwanted Greenhouse Gases Using a Kiln.

[0035]FIG. 1 illustrates a specific embodiment of the process and systemof the present invention in which a carbonaceous waste feed material ispassed via inlet line 10 to a non-catalytic high temperature, gas-phasereactor 12 and is converted into synthesis gas at high temperature inthe range of about 700° to about 1600° C. (1300-2900° F.). Preferably, arotary kiln is used as gasifier 12 having outlet 14 to remove thebuildup of solids. The syngas produced in gasifier 12 that leavesthrough outlet line 18 is then split downstream into two flow lines 20and 22. The syngas in flow line 20 enters fuel cell 26 at port 28. Thesecond syngas stream is passed via flow line 22 to Fischer-Tropschcatalytic reactor 30.

[0036] Preferably gasifier 12 is a slightly inclined horizontal rotarykiln that is heated externally and is called an “indirectly heatedrotary kiln.” The slight inclination encourages the feedstock to moveaxially along the rotary kiln away from the inlet as it is rotatedslowly. The carbonaceous feedstock or waste at or near room temperatureis introduced into one end of the kiln where the temperature is at about200° C. and it is subjected to increasing temperatures as it moves alongthe length of the kiln toward the gas exit end. Preferably thetemperature of the gas leaving the exit end is in the range of about1100° to 1600° C. (1650-2900° F.). Preferably this can be done bypulling the exit gases through a superheater of the type shown in FIG.11, which can be located in the region adjacent the exit end of the kilnshown in FIG. 12. The higher temperatures and added steam are needed toaccomplish the high levels of destruction required by U.S. EPA lawshould there be hazardous waste contaminant in a waste feedstock. Forrecovery of metals and glass for possible recycling, these solids areremoved from the kiln before they are melted. Preferably, these solidsare removed from the rotary kiln at solids exit 14, which is at anappropriate along the length of kiln where it is estimated that wastefeed has reached a temperature of about 400° C. (750°) and before thesolids have melted.

[0037] Examples of indirectly heated rotary kilns that are suitable forthe present invention are manufactured by: Von Roll Inc., 302 ResearchDrive, Suite 130, Norcross, Ga. 30092; Surface Combustion, Inc., 1700Indian Wood, Cir., Maunee, Ohio 43537; and Bethlehem Steel ofInternational Steel Group Inc., 3250 Interstate Drive—2nd Floor,Richfield, Ohio 44286.

[0038] In fuel cell 26, the syngas feed passes upward through theelectrolyte 40 around and through the porous catalytic anode electrode42 wherein the gases are oxidized electrochemically. Membrane 44 isionically conducting, but will not allow any of the gases or hydrocarbonspecies on either side of fuel cell 26 to pass through.

[0039] Examples of fuel cells that can accept syngas and are suitablefor fuel cell 26 of the present invention include the Solid Oxide FuelCell manufactured by Westinghouse, Monroeville, Pa. or by TechnicalManagement Inc., Cleveland, Ohio and the Molten Carbonate Fuel Cellmanufactured by FuelCell Energy Corp., Danbury, Conn. The pertinentportion of the following references are incorporated by reference intothis Detailed Description of the Invention: C. M. Caruana, “Fuel CellsPoised to Provide Power,” Chem. Eng. Progr., pp. 11-21, September, 1996and S. C. Singhal, “Advanced in Tubular Solid Oxide Fuel CellTechnology,” Proceedings of the 4th International Symposium on SolidOxide Fuel Cells, Pennington, N.J., Vol. 95-1, pp. 195-207 (1995).

[0040] The oxidized syngas, consisting essentially of hydrogen andcarbon monoxide, leaves anode 42 of fuel cell 26 mostly as water vaporand carbon dioxide. This stream of oxidized syngas passes via line 48into air-cooled condenser 50, where the water vapor is condensed intoliquid water and is removed from the condenser bottoms via line 52 forreuse. Wastewater recovered from a municipal sewage system can be usedin gasifier 12. However, all or a portion of the relatively pure waterin line 52 can be sold or recycled and combined with the wastewaterpassing into gasifier 12 via line 38. The carbon dioxide gas is notcondensed in condenser 50 and passes through into the condenser overheadas carbon dioxide gas to be fed back to the gasifier 12 via line 36. Thecarbon dioxide in high temperature gasifier 12 reacts therein with thecarbonaceous feed material to form more syngas to further assist in theoverall reaction. CO₂ or other greenhouse gases can be passed intogasifier 12 via line 56 to maintain the desired H/C ratio of thefeedstock.

[0041] To complete the description of FIG. 1, it is noted that the otherhalf-cell of fuel cell 26 involves air reduction on cathode 60. Thisstandard air electrode allows the entering oxygen-containing gas in line64, typically air, to pass upward through the air electrolyte 66 aroundand through electrode 60. The inert components of the air stream,consisting mostly of nitrogen, pass through the cathode half-cell andare removed via exit stream 68. Although more expensive, the cathodehalf-cell can also use pure oxygen instead of air to achieve higherefficiencies and more heat production. The fuel cell producessubstantial electrical power ranging from 4 to 9 kilowatts per standardcubic foot per minute of hydrogen feed.

[0042] In the Fischer-Tropsch catalytic reactor 30, the syngas in line22 is reacted over a catalyst 70 to form higher boiling hydrocarbons,such as waxes or other useful hydrocarbon products recovered in line 76.These waxes, for example, can form a feedstock to a Shell MiddleDistillates Synthesis Process where they are reacted to form naphtha,fuel gas, and kerosine, which are all valuable chemical products; see J.Eilers, S. A. Posthuma, and S. T. Sie, “The Shell Middle DistillateSynthesis Process (SMDS),” Catalysis Letter, 7, pp. 253-270 (1990). Thepertinent portions of this paper is incorporated by reference into thisDetailed Description of the Invention.

[0043] Thus, overall the carbon mass entering the feed via line 10leaves as carbon mass in the form of useful hydrocarbon products, whichare recovered, via line 76, thus avoiding the release of carbon dioxidewhen a hydrocarbon feedstock is gasified. There is no expensive andtroublesome alkali stripper to recover carbon dioxide from stack gases,as would be the case in a normal combustion/steam-turbine power plantconfiguration.

[0044]FIG. 2 is a plot of the commercial steam reforming of methane thatis a well known commercial process and is the principal process formanufacturing hydrogen gas in refineries for use in petroleumhydro-cracking and hydro-reforming process steps as well asmanufacturing hydrogen gas as a commodity sold in the marketplace.Standard nickel catalysts are used for this conversion in order to lowerthe reactor tube temperatures so that less expensive alloys can be usedand their process lifetime extended.

[0045] The plots shown in FIGS. 2-10 are based on calculations performedby the method of the Gibbs Free Energy Minimization to yield gascompositions at thermodynamic equilibrium from the lowest temperature of200° C. up to 2000° C. The chemistry is started by placing methane (CH₄)and steam (H₂O) at-one atmosphere in the gaseous (subscript, g) in avessel at 200° C. After waiting a sufficient amount of time, thecompounds react slightly and form a small quantity of hydrogen (H₂) andcarbon dioxide (CO₂) as shown in FIG. 2. This composition of the gasmixture is that which occurs if the chemical kinetics were fast enoughto allow the reaction to reach completion in the time allotted. Thefollowing two reactions are occurring simultaneously:

CH₄+2 H₂O→4 H₂+CO₂   (1)

H₂+CO₂→H₂O+CO   (2)

[0046] As soon as the H₂+CO₂ are formed in reaction (1), the “Water gasshift reaction” forms H₂O and CO by reaction (2).

[0047] In this way, reactions (1) and (2) interact according to each oftheir free energy driving forces to arrive at an equilibrium balance,and the final compositions are shown in the FIG. 2 As the temperature israised, the equilibrium shifts to forming H₂O and CO.

[0048] Practically speaking; however, commercially one cannot wait longperiods of time for the slow chemical kinetics at 200° C. to reach theequilibrium composition. The gas composition curves are achieved morequickly with less residence time when active surface catalysts are usedto impart extra energy into the gases to encourage them to react morequickly. As the temperature is increased, the kinetic velocities andenergies are increased by the increased kinetic activities of the gasescarrying more energy in their collisions and forming other compoundsmore quickly. Eventually, as the temperature is increased significantlyto say 600° C., the kinetics become so fast that no active surfacecatalyst is needed. Thus, the gas compositions shown in FIG. 2 can beachieved at temperatures above about 600° C. without the use ofcatalysts since the approach to thermodynamic equilibrium can beachieved in reasonable residence times. To make commercial H2, thecommercial embodiment carries out the gas-phase chemistry inside ofcatalyst-coated tubes or tubes filled with catalyst-coated ceramicbeads. These tubes are heated externally by means of very hot flue gasfrom a gas-fired furnace, sometimes using oxygen-enriched combustionair.

[0049] As the molecular complexity of the feed hydrocarbons increase,the temperatures have to be increased to levels well above 600° C. inorder to approach their chemical thermodynamic equilibrium compositionwithout the enhancing and accelerating effect of catalysts. In fact, ithas been found based on experimental testing and the simulationsperformed pursuant to the present invention that above 700° C. ispractically where catalysts are no longer needed when dealing withorganic wastes.

[0050] Commercial gasification processes for coal, coke, petroleum,organic waste and similar feedstock also use catalytic fixed orpreferably fluidized catalytic beds, such as the Texaco gasifier or theShell gasification process as discussed in the '465 patent. Thesecatalysts allow low enough temperatures that more cost-effective alloyscan be used at high pressures for these commercial gasification vessels.Wastes, such as those contemplated as feedstocks for the process of thepresent invention, contain contaminates that are catalyst poisons.Therefore, extreme care must be taken in the acceptance of such a broadclasses of wastes. The '465 patent discloses a preferred embodimentinvolving the use of a catalytic bed for gasifier 12 operating attemperatures in the range of about 400° to about 700° C. The wastes mustbe carefully selected so the catalysts are not easily poisoned whenwastes are used as feedstock and have halogen and heavy metalcontaminates.

[0051] Now introducing fuel cells into the process, FIG. 3 shows thesteam reforming of a mixture of methane and fuel cell-produced carbondioxide added into the feed at about 20%. In accordance to the teachingof the '465 patent, the gasifier preferably uses a catalytic bed to formsyngas. It has been found at high temperatures over 700° C., the syngascompositions shown are achieved without the need for catalysts.Comparing FIG. 2 and FIG. 3 beyond 800° C., it is noted that thehydrogen content is slightly lowered by the presence of increased carbonmonoxide and water that is formed and by the residual carbon dioxide,since all three act as significant diluents in the formed syngasproduct, diluting the hydrogen. In fact, the carbon dioxide has nopositive effect in the reaction, other than that it is consumed so thatit is not released to the environment.

[0052] These effects are even more exaggerated as shown in FIGS. 4-5 atcarbon dioxide concentrations of 25% and 30%, respectively. In thelatter case shown in FIG. 5, the hydrogen concentration is dropped downto 46.5% from the higher hydrogen of 58% with carbon dioxide increasedto 30% in the feed. But most importantly, in all these cases withincreased carbon dioxide, the hydrogen is found to drop gradually withincreasing temperatures over 800° C. where the thermodynamic equilibriumis achieved without the use of a catalyst.

[0053] Increasing the fraction of steam in the feed, as shown in FIG. 6,does not correct this problem, as one of ordinary skill in the art wouldhave thought. This situation, under conventional wisdom, dictated thatwith the use of lower temperature aided by the use of catalysts, thecatalysts were strongly preferred to maximize the hydrogen productconcentration desired. This was the dilemma faced by the inventor of the'465 patent.

[0054] Unexpectedly, a much-preferred solution has now been discoveredto optimize this fuel cell link that has been overlooked and notexploited previously. It involves using elevated steam feed and C0₂simultaneously with complex waste streams that have highercarbon/hydrogen ratios than simpler compounds such as methane. Thisapproach appears to be contrary to conventional wisdom and practice,which suggests that to achieve higher hydrogen concentrations at hightemperature, the worst option is to increase the carbon content of thefeed. However, this simplistic logic has been found to be very wrong.

[0055] The very simplified chemical reaction with the waste stream isfairly characterized entirely by carbon as in the following reaction:

3.8 C+0.6 CO₂+3 H₂O→>4.4 CO+3 H₂   (3)

[0056] Reaction (3) is already 68% by volume hydrogen (i.e. molepercent), which is far better than the hydrogen levels in FIGS. 3-6.Therein, one would have expected about 46% by volume H₂. Reaction (3)stoichiometry is the rough optimum, maximizing hydrogen content. Varyingthe stoichiometric quantities of the reactants produces less thanoptimum hydrogen. It is noteworthy that the addition of CO₂ to the feedreduces the requirements for steam below stoichiometric requirements. Infact, there is an optimum combination of using both CO₂ and steam.

[0057] A generalized chemical reaction can be written for anycarbonaceous feedstock, as expressed by the generalized empiricalformula C_(a)H_(b)O_(c):

5 C_(a)H_(b)O_(c)+D CO₂+(5a−5c−D) H₂O→(5a+D) CO+[5(a+0.5b+c)−D]  (4)

[0058] The H₂/CO ratio can be optimized by the right combination of CO₂and H₂O for a given waste feed mixture characterized by the empiricalformula, C_(a)H_(b)O_(c). It is noted that the amount of H₂O needed isreduced below its stoichiometric requirements (5a−5c) for conventionalsteam reforming by the “D” amount of CO₂ used, since the stoichiometriccoefficient on H₂O is (5a−5c−D).

[0059] Also, to help to adjust the H₂/CO ratio needed forFischer-Tropsch synthesis of useful chemical co-products to sequesterthe carbon and avoid greenhouse gas emissions, examining this H₂/COratio is helpful, since it is expressed as:$\frac{H_{2}}{CO} = \frac{{5\left( {a + {0.5b} + c} \right)} - D}{{5a} + D}$

[0060] One notes for a given carbonaceous feedstock with the empiricalformula, C_(a)H_(b)O_(c), one can adjust the amount of CO₂, “D”, tosatisfy the Fischer-Tropsch synthesis requirements.

[0061] To achieve higher hydrogen concentrations at high temperature todrive the fuel cells, increased feedstock hydrogen content together withan excess steam over stoichiometric levels, (5a−5c−D), is allowed and iscombined with the recycled fuel cell carbon dioxide, D. As shown inFIGS. 7-10, this provides the chemistry at thermodynamic equilibriumthat achieves a higher hydrogen-rich syngas that remains high and steadyin hydrogen over a broad high temperature range up to and beyond 1300°C. without catalysts.

[0062]FIG. 7 shows a plot of the steam reforming of a mixture of atypical industrial solvent waste (acetone, formaldehyde, methanol,dimethylbenzene, butanol, trichlor, and perchlor), without fuel cellproduced carbon dioxide added in the feed, but with steam at 49.45%. Asbefore, there are no kinetic limitations in compositions above 700° C.and the gas compositions are very accurate, and this fact has beenconfirmed by on-line gas chromatography and mass spectrometry. The H₂/COwas about 1.4. One notes that the hydrogen product remains high andsteady at 48.9% at 700° C. and beyond. However, the syngas is quitedirty; with many undesirable compounds at the 0.5 mole percent level(i.e. carcinogenic benzene). This syngas is not acceptable for moltencarbonate or solid oxide fuel cells even after the hydrogen chloride(and any other acid gases) are removed.

[0063] Referring to FIG. 7 at 1200° C., the syngas product compositionstarts at the highest with hydrogen, at 48.9%; then carbon monoxide at35.5%; methane at 6.3%; acetylene (C₂H₂) at 2%; hydrogen chloride gas at0.9%; benzene (C₆H₆) at 0.5%; ethylene (C₂H₄) at 0.4%; naphthalene at0.28%; propylene-1(C₆H₄) at 85 ppm; propylene-2 (C₃H₄) at 50 ppm; ethane(C₂H₆) at 25 ppm; methyl radical (CH₃) at 25 ppm; hydrogen radical at 9ppm; water at 7 ppm; carbon dioxide at 2 ppm; with all other compoundsat levels below 0.01 ppm.

[0064]FIG. 8 shows a plot of the steam reforming of the same mixture ofindustrial solvent waste as in the composition for FIG. 7, without fuelcell produced carbon dioxide added in the feed, but with steam at 66%.It is noted that the hydrogen product remains high and steady at 48.9%at 1000° C. and beyond. The syngas is quite clean, with undesirablecompounds at the 10⁻⁵ mole percent level (i.e. 0.1 ppm). This syngasratio H₂/CO of about 1.2 is excellent for Fischer Tropsch synthesis aswell as molten carbonate or solid oxide fuel cells, after the hydrogenchloride (and any other acid gases) are removed.

[0065] Referring to FIG. 8 at 1200° C., the syngas product compositionstarts at the highest with hydrogen, at 63%; then carbon monoxide at40%; hydrogen chloride gas at 0.6% ppm; water at 0.5%; carbon dioxide at0.1%; methane at 100 ppm; hydrogen radical at 10 ppm; acetylene at 4ppm; ethylene at 1 ppm; with all other compounds at levels below 0.09ppb. It is noted that this is only about 10,000 times cleaner in minorcontaminants where the goal of the present invention is a million timescleaner.

[0066] Even further improvements can be made, unexpectedly, as are shownin FIG. 9, by increasing the CO₂/H₂O ratio from the 1.3 in FIG. 7 up to2.8 in FIG. 9. This added CO₂ from the fuel cell is 25% of the wastefeed. The steam used in FIG. 8 is actually a decrease to 60% in theamount of steam consumption in the process, with the advantage of thesteam-reforming reactor being able to accept more CO₂, contrary toconventional thinking.

[0067] Referring to FIG. 9 at 1200° C., the syngas product compositionstarts at the highest with hydrogen, at 49.9%; then carbon monoxide at42.4%; water at 5.4%; CO₂ at 1.73%; hydrogen chloride gas at 0.6% ppm;hydrogen radical at 13 ppm; methane at 1.6 ppm; acetylene at 0.2 ppb;ethylene at 0.03 ppb; with all other compounds at levels below 0.1 ppb.It is noted that this is about 10 million times cleaner or lower inminor contaminants.

[0068] Even further optimizing improvements can be made as are shown inFIG. 10 by slightly increasing the recycle H₂O from the 46.3% in FIG. 9up to 50.9% in FIG. 10. This CO₂ from the fuel cell was 23% of the wastefeed. The syngas in FIG. 10 is actually cleaner.

[0069] Referring to FIG. 10 at 1200° C., the syngas product compositionstarts at the highest with hydrogen at 48.9%, then carbon monoxide at40.0%; water at 8.1%; CO₂ at 2.5%; hydrogen chloride gas at 0.6% ppm;hydrogen radical at 13 ppm; methane at 2.5 ppm; acetylene at 0.1 ppb;ethylene at 0.01 ppb; with all other compounds at levels below 0.04 ppb.It is noted that this is about 20 million times cleaner or lower inminor contaminants.

[0070] Both of these improvements shown in FIGS. 9 and 10 areeconomically attractive commercially. This yields a H₂/CO about 1.2 thatis a syngas composition more amenable to making more valuable chemicalco-products than methanol (selling only @50¢/lb), for example, thatrequires a H₂/CO of 2.0 for its synthesis. Thus, the addition of shiftreactors to adjust the H₂/CO upward or downward are not required—afurther economic advantage of this process of the present invention.

[0071] Referring to FIG. 11, a superheater 100 is shown in which amixture of air and natural gas or other suitable fuel is fed throughinlet 110 in gas feed tube 111 after fuel-air supply valve 112 is in theopen position to supply matrix burner 114. A suitable matrix burner isdescribed in U.S. Pat. No. 6,065,963, the description of which isincorporated herein by reference. Matrix or conical surface burners ofthe type suitable for use in the superheater of the present inventionare manufactured by N. V. Acotech S. A and Hauck Manufacturing Company.The flue gases from matrix burner 114 are removed from superheater 100via flue 114 in tube 116. Process gases from gasifier 12 enter through aplurality of process gas inlets 120 supplied by an annular manifold (notshown) around the circumference of the walls 122 of superheater 100 andpass into flow annulus 124. Similarly, steam is introduced through line150 (see FIG. 12) operably connected to a plurality of steam inlets 126supplied by an annular manifold into annulus 124. The heated exit gasespass through exit gas outlet 18.

[0072] Although FIG. 12 shows gasifier 12 comprising rotary kiln 130 andsuperheater 100 positioned partially within the exit region 138 of kiln130, superheater 100 can also be operably positioned entirely outside ofkiln 130 in order to superheat the intermediate gas stream from the kilnthat enter the process gas inlet 120 (see FIG. 11) of superheater 100 totemperatures in the range at least 700° to about 1600° C. (1300-2900°F.) before the exit gas stream passes through exit gas outlet 18. Astandard expansion bellows 139, a rotary seal assembly 140, and aplurality of pneumatic struts 142 are operably mounted around theoutside circumference of kiln 130 to allow for approximately one foot ofexpansion of kiln 130 during its operation.

[0073] Further, without departing from the spirit and scope of thisinvention, one of ordinary skill in the art can make various otherembodiments and aspects of the process and system of the presentinvention to adapt it to specific usages and conditions. As such, thesechanges and modifications are properly, equitably, and intended to be,within the full range of equivalents of the following claims.

What is claimed is:
 1. A process for converting carbonaceous feedstocks into energy without the production of unwanted greenhouse gas emissions comprising: (a) converting a carbonaceous feedstock selected from the group consisting of coal, hydrocarbon oil, natural gas, petroleum coke, oil shale, carbonaceous-containing waste oil, carbonaceous-containing medical waste, carbonaceous-containing military waste, carbonaceous-containing industrial waste, carbonaceous-containing medical waste, carbonaceous-containing sewage sludge and municipal solid waste, carbonaceous-containing agricultural waste, carbonaceous-containing biomass, biological and biochemical waste, and mixtures thereof, and a greenhouse gas stream in a gasification unit to synthesis gas comprising carbon monoxide and hydrogen, said gasification unit is a non-catalytic high temperature, gas-phase reactor operating at conditions to achieve a gas exit temperature of from at least 700° to about 1600° C. (1300-2900° F.); (b) electrochemically oxidizing at least a portion of said synthesis gas from said gasification unit in a first half-cell of a fuel cell (anode) to a first half-cell exit gas comprising carbon dioxide and water; (c) recovering the carbon dioxide from said first half-cell exit gas to serve as at least 20% of said greenhouse gas stream in step (a); and (d) electrochemically reducing an oxygen-containing gas in a second half-cell of said fuel cell (cathode) completing the circuit and resulting in the production of electrical energy.
 2. The process of claim 1 wherein said greenhouse gas stream is carbon dioxide.
 3. The process of claim 1 is used as in a waste-to-energy fossil fuel plant.
 4. The process of claim 1 is used in a petroleum refinery.
 5. The process of claim 1 is used in a petrochemical plant.
 6. The process of claim 1 Wherein said gasification unit contains a rotary kiln.
 7. The process of claim 1 wherein a portion of said synthesis gas from said gasification unit is converted in a chemical reactor into useful hydrocarbon products.
 8. The process of claim 7 wherein said chemical reactor is a Fischer-Tropsch reactor.
 9. The process of claim 1 wherein a major portion of the water is condensed from said first half-cell exit gas using a condenser.
 10. The process of claim 9 wherein CO₂ and at least a portion of the condensed water is passed to said gasification unit in an amount to adjust the hydrogen to carbon ratio of the combined carbonaceous feedstock and greenhouse gas stream is sufficient to result in a synthesis gas having an optimum ratio for the Fischer-Tropsch reactor.
 11. The process of claim 10 wherein said synthesis gas has a hydrogen to carbon ratio in the range of about 1.75 to about 2.5.
 12. The process of claim 1 wherein the amount of greenhouse gas stream is adjusted in step (a) so that the combined carbonaceous feedstock and greenhouse gas stream to said gasification unit has a hydrogen to carbon monoxide ratio in the range of about 1.75 to about 2.5.
 13. The process of claim 1 wherein the oxygen-containing gas in step (d) is air and the nitrogen portion as a result of the electrical reduction is exited into the atmosphere.
 14. The process of claim 1 wherein said first half-cell of said fuel cell contains an electrolyte surrounding a porous catalytic anode electrode.
 15. The process of claim 14 wherein said second half-cell of said fuel cell contains an electronically conducting electrolyte surrounding a catalytic cathode electrode.
 16. The process of claim 15 wherein said first and second half-cells of said fuel cell are separated by an ionically conducting membrane that will not allow passage of components from the respective half-cells.
 17. A system for converting carbonaceous feedstocks into energy without the production of unwanted greenhouse gas emissions which comprises: (a) a gasification unit containing a non-catalytic high temperature, gas-phase reactor and having inlet means for a carbonaceous feedstock selected from the group consisting of coal, hydrocarbon oil, natural gas, petroleum coke, oil shale, carbonaceous-containing waste oil, carbonaceous-containing medical waste, carbonaceous-containing military waste, carbonaceous-containing industrial waste, carbonaceous-containing medical waste, carbonaceous-containing sewage sludge and municipal solid waste, carbonaceous-containing agricultural waste, carbonaceous-containing biomass, biological and biochemical waste, and mixtures thereof, and a greenhouse gas stream operating at conditions to achieve a gas exit temperature of from at least 700° to about 1600° C. (1300-2900° F.) for converting a combined feedstock into synthesis gas comprising carbon monoxide and hydrogen and an outlet for the synthesis gas; (b) a fuel cell for the production of electrical energy comprising a first half-cell having an inlet in fluid communication with the synthesis gas and first means for electrochemically oxidizing synthesis gas into a first half-cell exit gas of carbon dioxide and water, a second half-cell having second means for electrochemically reducing an oxygen-containing gas, and a membrane separating said first and second half cells that will not allow passage of components from the respective half-cells; and (c) passage means for passing the carbon dioxide from said first half-cell to serve as a greenhouse gas stream for said gasification unit.
 18. The system of claim 17 wherein the greenhouse gas stream is carbon dioxide.
 19. The system of claim 17 wherein said gasification unit contains a rotary kiln.
 20. The system of claim 17 further comprising a chemical reactor in fluid communication with said gasification unit to convert a portion of said synthesis gas from said gasification unit into useful hydrocarbon products.
 21. The system of claim 20 wherein said chemical reactor is a Fischer-Tropsch reactor.
 22. The system of claim 21 wherein a condenser is used to condense a major portion of the water from said first half-cell exit gas.
 23. The system of claim 22 wherein the CO₂ and at least a portion of the condensed water is passed to said gasification unit in an amount to adjust the hydrogen to carbon ratio of the combined carbonaceous feedstock and greenhouse gas stream sufficiently to result in a synthesis gas having an optimum ratio for the Fischer-Tropsch reactor.
 24. The system of claim 23 wherein said synthesis gas has a hydrogen to carbon ratio in the range of about 1.75 to about 2.5.
 25. The system of claim 21 wherein the amount of greenhouse gas stream is adjusted in step (a) so that exit gas stream of said gasification unit has a hydrogen to carbon monoxide ratio in the range of about 1.75 to about 2.5.
 26. The system of claim 17 wherein the oxygen-containing gas is air and the nitrogen formed as a result of the ionic reduction is exited into the atmosphere.
 27. The system of claim 17 wherein said first half-cell of said fuel cell contains an electrolyte surrounding a porous catalytic anode electrode.
 28. The system of claim 27 wherein said second half-cell of said fuel cell contains an electronically conducting electrolyte surrounding a catalytic cathode electrode.
 29. A system for converting carbonaceous feedstocks into energy without the production of unwanted greenhouse gas emissions which comprises: (a) a gasification unit containing an indirectly heated rotary kiln and having inlet means for a carbonaceous feedstock selected from the group consisting of coal, hydrocarbon oil, natural gas, petroleum coke, oil shale, carbonaceous-containing waste oil, carbonaceous-containing medical waste, carbonaceous-containing military waste, carbonaceous-containing industrial waste, carbonaceous-containing medical waste, carbonaceous-containing sewage sludge and municipal solid waste, carbonaceous-containing agricultural waste, carbonaceous-containing biomass, biological and biochemical waste, and mixtures thereof, and a greenhouse gas stream, a gas exit means, and a solids exit means between the inlet means and the exit means operating at conditions to achieve a gas exit temperature of from at least 7000 to about 1600° C. (1300-2900° F.) for converting a converting the combined feedstock into synthesis gas comprising carbon monoxide and hydrogen and an outlet for the synthesis gas; (b) a fuel cell for the production of electrical energy comprising a first half-cell having an inlet in fluid communication with the synthesis gas and first means for electrochemically oxidizing synthesis gas into a first half-cell exit gas of carbon dioxide and water, a second half-cell having second means for electrochemically reducing an oxygen-containing gas, and a membrane separating said first and second half cells that will not allow passage of components from the respective half-cells; and (c) passage means for passing the carbon dioxide from said first half-cell to serve as a greenhouse gas stream for said gasification unit.
 30. The system of claim 29 wherein said gasification unit further comprising a superheater means for superheating the exit gas to a temperature in the range from at least 700° to about 1600° C. (1300-2900° F.).
 31. The system of claim 30 wherein said gasification unit comprises said indirectly heated rotary kiln having said inlet means for said carbonaceous feedstock, said gas exit means, and said solids exit means, and having said superheater operably positioned at least partially within said kiln in the region adjacent to the gas exit means. 